An over-temperature protection circuit for a direct current (DC) electric tool includes a current detecting circuit electrically coupled to a battery pack, a power device control circuit electrically coupled to an electric motor of the DC electric tool and a power device for controlling the power state of the circuit. A computation control circuit controls the power supply of the motor according to the circuit current value detected by the current detecting circuit. When the electric motor is not in a speed control state, the allowable current passing through the over-temperature protection circuit of the DC electric tool cannot exceed a preset first current value. When the electric motor is in the speed control state, the allowable current passing through the over-temperature protection circuit of the DC electric tool cannot exceed a preset second current value less than the first current value.